The New York commuter train which derailed at the weekend leaving four people dead was travelling at nearly three times the recommended speed limit when it hurtled off the tracks.

National Transportation Safety Board member Earl Weener said the train involved in Sunday's accident in the Bronx had clocked 82 miles (131 kilometres) per hour as it entered a curve where the limit was 30 miles (48 kilometres) per hour.

Investigators also found that shortly before the crash the train's throttle had gone to idle and there had been a sudden loss in brake pressure.

"Our investigators will be carefully reviewing all the data to determine the functioning of the brakes throughout the trip and to determine why the throttle went to zero, brake pressure went to zero," Mr Weener said.

"At this point, we are not aware of any problems or anomalies with the brakes."

The train, carrying between 100 and 150 people, crashed about 7:20am (local time) on Sunday as it headed south to Grand Central Station in Manhattan.

The train's seven cars derailed just before it reached Spuyten Duyvil station and flew across a grassy bank separating the railroad from the Hudson and Harlem rivers, which meet at that point.

The front car came to rest less than a metre from the water and two cars toppled on their side.

Mr Weener said investigators had begun questioning the driver and would continue to do so over the coming days.

Governor says speed was most likely a factor

New York governor Andrew Cuomo says the cause of the crash, which also left 67 people injured, is most likely "speed-related," noting the stretch of track involved in the accident is "tricky" but not especially hazardous.

"This was a tricky turn on the system, but it's a turn that's been here for decades and trains negotiate all day long," he told NBC.

"I think it's going to turn out to be about the speed more than anything, and the operator's operation of the train at that time."

Mr Cuomo later described the horror passengers experienced as the train skidded at high speed before coming to a rest.

"The windows broke out, the doors opened and they were picking up stones, rock, dirt, tree limbs were flying through the cars," he said.

Some passengers were "impaled" by debris as train cars flew into the air, officials have said, while others had to be cut free from tangled metal.

The Metropolitan Transportation Authority identified the four victims, who ranged in age from 35 to 59. Two were men, two were women, and all were New York-area residents.

Three of the victims had been thrown from the train.

Commuter rail service in the area around the accident remained suspended on Monday.